It is known to fabricate an electric wire comprising a copper alloy conductor that is protected by a PTFE-based sheath. The wire is fabricated by forming a PTFE-based sheath around the copper alloy conductor.
If a “bare” conductor is used in such fabrication, i.e. a conductor that is not covered in an outer coating to protect it against oxidation, then during steps of lubricant evaporation and of sintering the PTFE sheath, a thin layer of copper oxide forms around the copper alloy conductor. Such an oxide layer is easily visible since it generally has a color that is quite different from that of copper. As a result of this oxide layer, the appearance of the copper is dark red or even black.
With such a conductor, the potential for soldering or for electric or ultrasonic welding is reduced, and contact resistance is high after crimping to connector elements.
That is why, in practice, no electric wire is fabricated in that way using a “bare” conductor. On the contrary, in order to avoid such problems, and in known manner, instead of using a bare copper alloy conductor, a copper alloy conductor is used that is also covered in an outer coating to protect it against oxidation. Such a coating is commonly a layer of silver or of nickel that is interposed between the atmosphere outside the wire and the conductor, so as to prevent any oxidation of the conductor. Naturally, applying such a coating leads to considerable extra cost for the conductor, and to increased complication in its method of fabrication.
A section of an electric wire having those characteristics is shown in FIG. 1. The electric wire 1 thus comprises a central conductor 11 of circular section, covered by an outer coating (anti-corrosion surface coating) 12, e.g. a layer of silver. The assembly is protected by an outer sheath 13 of substantially constant thickness that is based on PTFE.
With a wire having that structure, and by virtue of the anti-corrosion coating 12, no copper oxidation occurs at the surface of the conductor 11 during the steps of evaporating the lubricant and sintering the PTFE, which steps are performed after the PTFE sheath has been formed. However, having recourse to an anti-corrosion coating 12 leads to a method that is less simple and more expensive.